Silicone resins comprise three-dimensional networks which are made up of trifunctional or tetrafunctional silicon units R.sup.1 SiO.sub.3/2 or SiO.sub.4/2, where R.sup.1 is selected from the group consisting of aliphatic or aromatic hydrocarbon radicals. In addition, linear units R.sup.1.sub.2 SiO and/or monofunctional units R.sup.1.sub.3 siO.sub.1/2 may also be present The hydrolysis of trifunctional chlorosilanes or silicon tetrachloride with water leads to a high proportion of gel in the hydrolysate, even when the hydrolysis is carried out in the presence of organic solvents such as toluene and acetone.
The preparation of resin from partially alkoxylated chlorosilanes or alkoxysilanes described in DE-A873 433, in which the formation of gel is greatly reduced, was introduced a long time ago. The hydrolysis results in the resin product plus an alcohol-containing aqueous phase comprising the hydrochloric acid formed from the chlorosilanes as well as residues of silicone resin and amounts of gel.
In order to make resin production economical and to avoid waste, it is of great interest to recover the alcohol used from the aqueous phase simply and as completely as possible. The greatest problem in the work-up of this process stream is posed by the amounts of resin and gel. If the alcohol is distilled from the mixture in a pot still or distillation column, deposits of accumulating silicone resin are formed on the heat exchangers after a short time and these hinder heat transfer and have to be removed periodically. Even when steam is injected directly, deposits on the walls are formed from the amounts of gel under acid conditions.
A further problem in the work-up of the aqueous-alcoholic phase is in many cases the acid which is necessary as condensation catalyst. Since hydrochloric acid which is formed in the hydrolysis of the partially alkoxylated silanes is frequently used, readily volatile alkyl halides are formed from the alcohols and HCl on heating and these in turn cause emission problems.
Steam stripping of organic-containing wastewater is used to remove volatile organic constituents. Hwang, Y.-L. et al.; Ind. Eng. Chem. Res. 1992, 31, 1753-1759 and Hwang Y.-L. et al.; Ind. Eng. Chem. Res. 1992, 31, 1759-1768 give the necessary criterion for successfully carrying out steam stripping of wastewater as a vapor-liquid equilibrium constant at infinite dilution K.sup..Yen. &gt;1. Alcohols have low K.sup..Yen. values, e.g. ethanol -0.4 and methanol -0.5. Hassan, S. Q.; J. Air Waste Manage. Assoc., 1992, 42, 936-943 gives the criterion for successfully carrying out steam stripping as a solubility of the organic constituent in water of at most 1000 ppm. Steam stripping is accordingly completely unsuitable for removing alcohols such as ethanol or methanol from an aqueous solution.
DD-A-228 550 describes the recovery of alcohol from the aqueous-alcoholic hydrochloric acid which is obtained in the preparation of methylsilicone resins by passing in steam, however, it does not describe how the process is carried out and how gel deposits occurring in the hydrochloric acid medium and the alkyl chloride emissions can be avoided.